+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE StandaloneDeriving #-}
+
+-- | An OptionalConfiguration is just like a 'Configuration', except
+-- all of its fields are optional. The user can set options in two
+-- places: the command-line, and a configuration file. Obviously if
+-- a parameter is set in one place, it doesn't need to be set in the
+-- other. Thus, the latter needs to be optional.
+--
+module OptionalConfiguration (
+ OptionalConfiguration(..),
+ from_rc )
+where
+
+-- System imports.
+import qualified Data.Configurator as DC (
+ Worth(Optional),
+ load,
+ lookup )
+import Data.Data ( Data )
+import Data.Maybe ( fromMaybe )
+import Data.Monoid ( Monoid(..) )
+import Data.Typeable ( Typeable )
+import Paths_harbl ( getSysconfDir )
+import System.Console.CmdArgs.Default ( Default(..) )
+import System.Directory ( getHomeDirectory )
+import System.FilePath ( (</>) )
+import System.IO.Error ( catchIOError )
+import System.IO ( hPutStrLn, stderr )
+
+-- Local imports.
+import Hosts ( Hosts(..) )
+import Lists ( Lists(..) )
+
+
+-- | The same as 'Configuration', except everything is optional. It's
+-- easy to merge two of these by simply dropping the 'Nothing's in
+-- favor of the 'Just's. The 'xml_files' are left un-maybed so that
+-- cmdargs can parse more than one of them.
+--
+data OptionalConfiguration =
+ OptionalConfiguration {
+ hosts :: Hosts,
+ lists :: Lists }
+ deriving (Show, Data, Typeable)
+
+
+-- | The Monoid instance for these lets us \"combine\" two
+-- OptionalConfigurations. The \"combine\" operation that we'd like to
+-- perform is, essentially, to mash them together. So if we have two
+-- OptionalConfigurations, each half full, we could combine them
+-- into one big one.
+--
+-- This is used to merge command-line and config-file settings.
+--
+instance Monoid OptionalConfiguration where
+ -- | An empty OptionalConfiguration.
+ mempty = OptionalConfiguration (Hosts []) (Lists [])
+
+
+ -- | Combine @cfg1@ and @cfg2@, giving precedence to @cfg2@.
+ -- XML files can only be specified on the command-line, so we
+ -- just join them together here.
+ cfg1 `mappend` cfg2 =
+ OptionalConfiguration all_hosts all_lists
+ where
+ all_hosts = Hosts $ (get_hosts $ hosts cfg1) ++ (get_hosts $ hosts cfg2)
+ all_lists = Lists $ (get_lists $ lists cfg1) ++ (get_lists $ lists cfg2)
+
+
+
+-- | Obtain an OptionalConfiguration from harblrc in either the global
+-- configuration directory or the user's home directory. The one in
+-- $HOME is prefixed by a dot so that it is hidden.
+--
+-- We make an attempt at cross-platform compatibility; we will try
+-- to find the correct directory even on Windows. But if the calls
+-- to getHomeDirectory/getSysconfDir fail for whatever reason, we
+-- fall back to using the Unix-specific /etc and $HOME.
+--
+from_rc :: IO OptionalConfiguration
+from_rc = do
+ etc <- catchIOError getSysconfDir (\e -> do
+ hPutStrLn stderr (show e)
+ return "/etc")
+ home <- catchIOError getHomeDirectory (\e -> do
+ hPutStrLn stderr (show e)
+ return "$(HOME)")
+ let global_config_path = etc </> "harblrc"
+ let user_config_path = home </> ".harblrc"
+ cfg <- DC.load [ DC.Optional global_config_path,
+ DC.Optional user_config_path ]
+ cfg_lists <- DC.lookup cfg "lists"
+ let cfg_hosts = Hosts [] -- This won't be in the config file.
+ return $ OptionalConfiguration cfg_hosts (fromMaybe def cfg_lists)